Volume 11, Issue 11
June 6, 2003
Volume 11, Issue 11
June 6, 2003
Vegetables
Vegetable Insects
-
Melons.
Continue to scout all melons for aphids, cucumber beetles, thrips and spider mites. Economic levels of melon aphids can be found and cucumber beetle populations have also reached threshold levels. In many cases, beneficial insect activity has significantly increased and can eliminate aphid populations. The treatment threshold for aphids is 20% of the plants infested with at least 5 aphids per leaf. Actara, Fulfill, Lannate and Thiodan are the labeled on melons and will provide melon aphid control. The treatment threshold for cucumber beetles in watermelons is 2 per plant. Carefully check field margins, under plastic, and cracks in ground around the base of plants for beetles. Since cucumber beetles vector bacterial wilt in cantaloupes, treatments should be applied before adult beetles feed extensively on cotyledons and first true leaves. Actara, dimethoate, or a pyrethroid will provide cucumber beetle control.
Peppers.
In addition to thrips and corn borers, we have had reports of aphids feeding on peppers. A mixture of potato and green peach aphids can be found. Where Admire was used at planting, we are not seeing aphids. A treatment may be needed prior to fruit set if you find 1-2 aphids per leaf for at least 2 consecutive weeks and beneficial activity is low.
Potatoes.
Continue to sample fields for Colorado potato beetle adults and larvae. The treatment threshold for adults is 25 beetles per 50 plants and 10% defoliation. Once larvae are detected, the threshold is 4 small larvae per plant or 1.5 large larvae per plant. If multiple life stages are present, reduce these thresholds by one-half. Actara, cryolite, Spintor or Provado will provide control. A corn borer spray will be needed when we reach 700-degree days (base 50). Currently we have only accumulated 504 degree-days. If we see an increase in temperatures, the first spray should be needed in the next 7-10 days. Be sure to check our website (http://www.udel.edu/IPM/traps/latestblt.html) for the most recent moth catches in your area. Ambush, Baythroid, Furadan, Penncap, Pounce or Spintor will provide control. If you are scouting for infested terminals, the first treatment should be applied when 20-25% of the terminals are infested. Furadan or Monitor will provide the best control if you are waiting until you see infested terminals. Potato leafhoppers populations remain light. Controls should be applied if you find ½ to one adult per sweep and/or one nymph per every 10 leaves. Dimethoate, a pyrethroid, Actara or Provado will provide control. In most cases, beneficial insects have helped to clean up potato aphid populations.
Snap
Beans.
Continue to scout seedling stage fields for leafhopper and thrips activity. The thrips threshold is 5-6 per leaflet and the leafhopper threshold is 5 per sweep. If both insects are present, the threshold for each should be reduced by 1/3. Dimethoate, Lannate, Asana, Capture, or Warrior will provide control of both insect pests. As soon as the earliest planted fields begin to bloom, Orthene should be applied for corn borer control, especially if trap catches exceed 2 per night.
Sweet Corn.
Corn borer whorl infestations remain light - 5-10% infested plants. A treatment should be applied if 15% of the plants are infested. The best timing for a treatment is just as the tassels are emerging from the whorls. In recent years, Baythroid, Mustang, Penncap or Warrior have provided effective control. If corn was planted under plastic, the first silk sprays will be needed as soon as ear shanks are visible. Treatment will be needed on a 6-day schedule throughout the state.
We are also seeing cereal leaf beetle adults in seedling and whorl stage corn. A treatment may be needed if you find 10 beetles per plant and 50% of the plants exhibit damage.
Vegetable Crop
Diseases –
Potatoes.
The rainy, cool weather pattern is certainly favorable for some foliar diseases. If late blight was present in seed producing areas it would be a real threat under these conditions, fortunately it is not. The high winds we experienced this past week or any other type of damage to the foliage such as hail can damage leaves and open them for infection by secondary fungi such as Botrytis or Alternaria alternata or others. So protecting the crop with fungicides such as mancozeb or chlorothalonil at this point is beneficial. If pink rot control is important and you did not treat at planting, foliar applications of either Ridomil Gold MZ or Ridomil Gold/Bravo, or Flouronil when tubers are nickel-sized is suggested. A second application should be made 14 days later. Conditions are not favorable for early blight, but if the crop runs out of nitrogen early because of the amount of rain we have had, fungicides for early blight control may be needed earlier than normal. Quadris, Gem or Headline would be the most effective for early blight, and black dot applied at the end of flowering and repeated 14 days later.
Field Crop Insects
-
Alfalfa.
Potato leafhopper populations remain light. Continue to sample fields for potato leafhopper adults and nymphs. The treatment thresholds are 20 per 100 sweeps on alfalfa 3 inches or less in height, 50 per 100 sweeps in 4-6 inch tall alfalfa and 100 per 100 sweeps in 7-11 inch tall alfalfa. Baythroid, dimethoate, Mustang or Warrior will provide effective control.
Field Corn.
Continue to sample no-till fields for true armyworm. We continue to find fields with above threshold levels. The treatment threshold for armyworms in corn is 25% infested plants with larvae less than one-inch long. A pyrethroid will provide effective control, but only if worms are less than one-inch long.
Unfortunately, slugs are still the number one pest in many no-till corn fields. The only available control options are liquid nitrogen applied at night when the plants are dry or the metaldehyde baits (Deadline MPs or TrailsEnd LG). A few days of sunny warm weather would help cure a lot of problems including the slugs!
Small
Grains.
In most cases, the decision to treat cereal leaf beetle
should have already been made and we can now find adults moving into
surrounding fields. Aphid populations are still high in some fields throughout
the state. Fields should be scouted for aphids through the soft dough stage.
The treatment threshold for aphids is 20-25 per head with low beneficial
activity (less than 1 per 50 aphids).
Beneficial insect activity including parasites, lady beetles and syrphid
fly larvae, has increased in some fields. Be sure to watch for these predators
since they can quickly reduce populations. Although grass sawfly and armyworm
populations remain low, we have had a report of economic levels in a field in
Soybeans.
With the wet field conditions and delayed soybean planting, a seed treatment for seed corn maggot should be considered in all fields. Materials containing permethrin, such as Kick-Start VP and Kernel Guard Supreme have provided effective control. Although very few fields are planted and emerged, be sure to watch for bean leaf beetle at emergence. A treatment for bean leaf beetle will be needed from plant emergence to the second trifoliate when you find 2 beetles per ft. row and a 25% stand reduction. A pyrethroid or dimethoate will provide effective control.
Field Crop
Diseases –
Wheat.
Sepotria leafspot
continues to be the most widespread disease currently. After looking at our
variety plots in
Barley.
Spot blotch form of net blotch is the predominate disease in
barley at
Here are more pictures of these diseases on wheat and barley. Last week some of the pictures were not properly identified.
Wheat:
Septoria nodorum is currently found in
Speckled leaf blotch
caused by Septoria tritici
is very similar and found in
Barley:
Net blotch. This
classic symptom was seen in
Spot blotch form of net blotch on barley in
Soybeans.
Septoria leafspot is present on the unifoliate leaves of early planted (April 22) soybeans. When the weather changes this disease should subside.
Septoria on Soybean
Grain Marketing Highlights -
Rain Makes Grain.
It is possible that the old adage "rain makes grain"
could become the rallying cry in the commodities market this next week. The
Weekly Exports Send Mixed Signals.
The weekly export sales report issued on June 5 was moderate
for old crop soybean sales, mid-range to trade expectations at 111,800 MT.
There were no new crop sales in the mix, all old crop. The trade was expecting
to see some evidence of new crop sales.
Corn sales at 533,900 MT were just below the low side of
trade expectations. This level is not likely to provide much impetus for
positive price action between now and the release of the next USDA crop report.
New crop corn sales totaled 43.1 MT.
Combined old/new crop
Next Crop Report.
USDA's June crop report will be released on Wednesday, June
11th at
Identifying
Lightening Injury in Corn -
With the continuation of the current weather pattern, some growers, consultants, and agents are being called on to identify small, usually circular spots in corn fields. These areas often show a small number of dead or dying plants in their center and are surrounded by many more plants that are lodged or twisted to some degree. In Photo 1, you can see the roughly circular area with about 10 dead plants in the center. Plants outside the initial kill zone showed injury at the soil line resulting in an inability of the stalk or leaf whorl to hold the plant upright (Photo 2).
Photo 1.
Dead plants in the center of a damaged area surrounded
by plants showing damage at the soil level following a lightening strike (Photo
by
Photo 2.
Corn plants outside the kill zone showing injury at the soil line
resulting in severe lodging (Photo by
In this instance, the grower remembers lightening hitting the field narrowly missing an irrigation system parked a mere 70 feet away. The strike likely occurred during a period of heavy rain that resulted in the area being ponded since the field is quite sandy and usually does not have standing water very long after rain stops. It was estimated that about one-twenty fifth of an acre was affected by the lightening strike. Photo 3 and 4 will give you a wider view of the damage to help you identify this type of damage when you see it.
Photo 3.
Lodged corn plants showing a roughly circular pattern
in a field following a lightening strike (Photo by
Photo 4.
Lodged corn plants in a field following a lightening
strike that luckily missed a nearby irrigation system (Photo by
Decision Criteria
for Planting Corn Late - Richard W.
Taylor, Extension Agronomist;
In a field meeting this past Tuesday at
There are some suggested practices if you do plant more corn in the next couple of weeks. You should try to stick with hybrids that have a relative maturity of about 105 to 110 days or less if planting towards the end of the window. Late planted corn often attracts more insect problems, so it is important to use a Bt hybrid to help control corn borer problems. The insect problem is usually worse when there is a large difference in the size of the late planted and early planted corn. Unless something changes or you are unable to plant until long after warm weather occurs, this year there may not be as big a difference between late-planted and early-planted corn. This may lessen the potential damage from insects, but it will not eliminate the problem.
Another concern as you switch to earlier maturing hybrids is their disease resistance package. Late-planted corn frequently shows more stress from corn diseases than early-planted corn, so always choose a hybrid with the best possible disease resistance package when planting it late.
In a recent article, Dr. Bob Nielsen from
Another question raised was whether to boost or reduce the seeding rate. If you could predict the weather and were assured it would rain all summer, then you might choose an irrigated population as target. Since I don’t know, my suggestion is to keep the same seeding rate as you normally use for your corn plantings.
When should you consider switching? My advice is that some time between June 20-25th you should seriously consider moving to soybeans assuming your herbicide program does not preclude rotating to soybeans.
This does bring up another question. If you have already applied your herbicide program or if you have to come in to replant a field that has been sprayed with herbicides, you will be constrained as to what crop you can seed. Be sure to take into account limitations such as this when making decisions. Also, if you have applied manure or N fertilizer to a field that you switch away from corn and to soybeans, you should keep in mind some of the problems that can occur. We have found that where manure has been applied and a soybean crop is planted, there can be a yield reduction if the supply of N from the manure runs out during early pod fill. Where high soil N levels exist, nodulation of the soybeans is weak. If the soil N supply suddenly becomes inadequate during flowering and early pod fill, the time lag between the need for N fixation and how quickly the nodules can form and begin to fully function is enough to cause limitations on yield potential.
Keep Close Watch
on Corn for Nitrogen Stress - Richard W.
Recent intense rainfall in some areas of the state could lead to nitrogen (N) stress in emerged corn fields. When soils become saturated with water, N that is in the nitrate form can undergo a biological process called denitrification. In this process, certain soil anaerobic bacteria convert nitrate-N to reduced forms such as N2, NO, and N2O which bubble out of the soil in a gaseous state. Generally, the process is temperature dependent with only 1 to 2 percent of nitrate-N denitrified per day (when the soil is saturated), if the temperature is less than 55˚ F, but 4 to 5 percent denitrified per (saturated) day if the soil temperature is above 65˚ F.
Most of us apply a small amount of N (20 to 30 lbs N/A) as a starter to keep the crop growing until sidedress time. This year soil temperatures have remained lower than normal restricting the amount of N mineralized from the soil organic matter (SOM) which supplements what is applied as starter. For corn that has been planted for a month or more, much of the N has been converted into the nitrate form of N even if it was originally applied as the urea, ammonium, or other reduced form of N. Even at the 1 to 2 percent rate of denitrification, we are likely to be losing from ¼ to ½ pound of N per acre per day of saturated conditions. Even when the entire field is not saturated, there will be areas where saturated conditions exist on the small or micro-scale.
On sandy soils, the leaching of N below the rooting zone is also of concern. Because of the wet conditions and lack of sun to warm the deeper layers of soil, it is likely that root development has been limited up to this point in the season. There is a strong possibility that much of the N applied up to this point has leached below the corn’s rooting zone.
During the next few weeks, carefully observe your corn fields to identify as soon as possible any symptoms of N deficiency stress in the corn. If symptoms appear (usually they first appear on the oldest leaves), consider applying at least part of the remaining N requirement right away to get the crop growing again. I would suggest that you consider adding only a portion of the total planned N rate if the crop is still very small. If the weather suddenly warms up and we receive plenty of sunlight, a disorder called rapid growth syndrome or twisted whorl syndrome can occur. Typically, it occurs when periods of slow corn development (from planting to the current date) are followed by a rapid change to a period of rapid corn development (warm, sunny weather, plenty of soil moisture and excellent soil nutrient status). It can affect entire fields or individual plants, but usually doesn’t show up until after corn plants are showing 5 to 6 leaf collars. Often the whorls of the affected plants will appear tightly twisted and can bend over at almost right angles. Plants usually have difficulty breaking out of the twisted whorl and when they do the new leaves will be very light in color or almost yellow.
Limiting N additions, or where irrigation is available, applying N on an as needed basis can prevent the abrupt change from slow development to very rapid development. You may see some differences among hybrids in their susceptibility to this problem.
Update on Last Week’s Soil-Applied Herbicide Table
-
Last week I included a table for how late soil-applied
herbicides can be applied. The labels
for Python and Hornet have been changed lately and they can be applied to corn
up to 20 inches tall. Also, keep in mind,
just because a herbicide is labeled for use on emerged corn, it does not mean
that the herbicide will provide residual control. Refer to pesticide labels or Delaware
Pesticide Guides for level of control you can expect from a herbicide on
emerged weeds.
Burndown Control for No-Till Soybeans -
Due to the rains, many no-till soybean fields have not been
sprayed. Note that Gramoxone labels list
maximum weed size of 6 inches, Roundup labels list winter annual weed sizes
from 6 to 18 inches (maximum size differs for weed species and rate), and most
2,4-D labels do not list maximum weed size.
The long and short of it is that most of these fields have weeds larger
than the labels recommend and it will be difficult to achieve good control.
Careful of Surfactant Use in this Weather -
Due to overcast
skies and ample moisture plants have very thin cuticles which may result in
increased injury with postemergence herbicides.
Nitrogen additives are most likely to cause crop injury with this
weather. Also, consider using non-ionic
surfactant rather than crop oils to reduce the risk of injury.
Rainfastness
and Maximum Corn Size for Postemergence Herbicides -
Rainfastness is number of hours needed between time of
application and rainfall or irrigation to ensure sufficient absorption in the
plant.
Broadcast
applications refer to an over the top application and directed refers to use of
special spray equipment to direct the spray and avoiding the spray coming in
contact with the whorl of the corn. When corn height and collar number are given,
base decision on whichever feature is first attained.
|
Herbicides |
Rainfast interval (hr) |
Maximum corn size
|
|
Accent |
4 |
broadcast: 6 collars or 20 in. directed: 10 collars or 36 in. |
|
Aim |
1 |
broadcast:
up to 8 collars directed: when necessary |
|
Atrazine |
2 |
12 inches tall |
|
Banvel Clarity |
4 |
more than
½ pt/A: broadcast: 5 lvs or 8 in. directed: 36 inches tall ½ pt/A or less: 36 inches tall |
|
Basagran |
8 |
No restrictions listed |
|
Beacon |
4 |
broadcast:
min- 4 inches tall max- 20 in. tall or 6 collar directed: pre-tassel |
|
Buctril |
1 |
pre-tassel |
|
Callisto |
1 |
30 inches tall or 8 collars |
|
2,4-D
Amine |
6-8 |
broadcast:
8 inches tall directed: pre-tassel |
|
2,4-D
Ester |
2-3 |
broadcast:
8 inches tall directed: pre-tassel |
|
Evik |
- |
directed only: 12 inches tall do
not apply 3 weeks before tasseling |
|
Harmony
GT |
1 |
1 - 4
collars or 12 inches tall |
|
|
4 |
broadcast:
24 inches tall or 7 collars directed: 20 to 36 inches tall |
|
Option |
2 |
broadcast:
16” tall or V5 directed:
16-36” tall |
|
Permit |
4 |
broadcast:
48 inches tall directed: when necessary |
|
Poast Poast
Plus |
1 |
broadcast:
emergence to start of pollen shed directed: when necessary
(depending on corn canopy and weed ht.) |
|
Resource |
1 |
broadcast:
2- to 10-lf collars directed: when necessary; when
corn leaves interfere w/ spray |
|
Roundup
products |
1-6 |
up to 30 inches or 8 collars |
|
Stinger |
6-8 |
24 inches tall |
|
Touchdown |
- |
up to 8 collars |
|
Tough |
1-2 |
until 68 days pre-harvest |
|
Premixes |
|
|
|
Basis |
4 |
2 collars or 6 inches tall |
|
Basis
Gold |
4 |
5 collars or 12 inches tall |
|
Celebrity
Plus |
4 |
broadcast: 4 to 24 inches tall |
|
Distinct |
4 |
6 oz
rate: 4 to 10 inches tall 4 oz
rate: up to 24 in. tall directed: 4 oz up to 36 inches tall |
|
Exceed |
4 |
broadcast:
min- 4 in. tall max- 20 in. tall or 6 collar directed: 20 to 30 inches tall |
|
Field
Master |
2 |
do not apply to emerged corn |
|
Hornet
WDG |
6 |
broadcast:
20 inches tall or 6 collars directed: 20 to 36 inches tall |
|
Laddok |
8 |
12 inches tall |
|
|
4 |
12 inches tall |
|
Lightning |
1 |
broadcast:
12 inches tall directed: 20 inches tall |
|
Marksman |
4 |
broadcast: 5-lf stage or 8 inches tall |
|
Northstar |
4 |
broadcast:
min- 4 inches tall max- 20 in. tall or 6 collar directed:
20 to 30 inches tall |
|
Ready Master ATZ |
2 |
emergence
until 12 inches tall |
|
Shotgun |
24 |
broadcast:
8 inches tall directed:
12 inches tall or if rate >2 pts |
|
Spirit |
4 |
broadcast: 20 inches tall or
6 collars (min. 4 in. tall) directed:
20 to 24 inches tall (before tassel emerg.)
|
|
Steadfast |
4 |
less than 20 inches or 6
collars |
|
|
4 |
spike through 36 inches tall |
an “-“ means
no information on label
Weeks of May 30 to
|
|
Rainfall: |
|
0.09 inches: May 31 0.03 inches: June 1 0.06 inches: June 3 0.37 inches: June 4 |
|
|
|
Air Temperature: |
|
Highs Ranged from 78°F on
May 30 to 64°F on June 1 |
|
Lows Ranged from 61°F on May
31 to 49°F on June 2 |
|
Soil Temperature: |
|
66°F average for the week. |
|
(Soil temperature taken at
a 2 inch depth, under sod) |
Web Address for the U of D
Compiled and Edited
By:
Extension Associate -
Vegetable Crops
Cooperative Extension Education in Agriculture
and Home Economics, University of Delaware, Delaware State University and the
United States Department of Agriculture cooperating. Distributed in furtherance
of the Acts of Congress of May 8 and